The invention relates generally to apparatus for heating wet or curing concrete and, more particularly, to apparatus for heating a concrete form or blanket to speed the curing time of freshly poured concrete adjacent the form or blanket.
Concrete is, of course, a ubiquitous building material due to its low cost, high strength in compression, durability, and adaptability to a wide variety of geometries. Concrete may either be pre-cast at a site remote from where it is to be installed or may be cast in place typically through the use of reusable concrete forms. Particularly when being cast in place, the concrete is subject to the environmental conditions of the construction site at the time of construction. Unless protected in some manner, the curing concrete is, accordingly, subject to less than optimum curing conditions, such as rain, cold, heat, humidity, and so forth. The cure time, strength during curing, and final strength of the concrete are all functions of these environmental conditions.
Of particular concern is the inverse relationship between curing time and temperature. That is, the lower the temperature, in general, the longer the time it takes for the concrete to cure. At sufficiently low temperatures, moreover, the water in the fresh concrete may freeze. The frozen water may result in heaving of the partially set concrete and its surrounding forms. Further, the water in its frozen state will not be available as required for curing of the concrete.
While heating of curing concrete may be required under certain conditions because of excessively low ambient temperatures, heating may also be done in warmer conditions where it is desired to accelerate the strength gain in the curing concrete. Strength gain and curing time are the primary factors which affect the turn-around time of concrete forming apparatus. Only when the curing concrete has reached a sufficient strength and state of cure may the forms be stripped for reuse in another section of the structure. Turn-around or recycle time is of particular concern in civil engineering projects, such as bridges, where the structure will be closed to use during construction.
Current methods of heating fresh or curing concrete typically employ make-shift temporary structures having a relatively large interior volume that is heated with portable heaters. The framework of these temporary structures is usually constructed from scrap frame lumber which is loosely covered with a sheet material such as polyethylene. The Construction of these temporary structures makes inefficient use of labor and have heat losses commonly in the range of 95 percent. The cost of labor and materials often preclude the building of higher quality shelters with adequate insulation and air seals. Accordingly, the prior art systems suffer from the defects of a high cost of construction, high maintenance due to weather damage, the necessity of alterations to provide access to the interior, high energy losses due to lack of insulation and the infiltration of cold air or escape of hot air, unequal heat distribution resulting in cold air at the bottom of the enclosure where the majority of the concrete is usually found, and the impairment of safety due to reduction in air quality and increased risk of fire.